With multi-stage centrifugal pumps, with which the impellers of the pump stages are arranged on a common shaft and are rotatably arranged within a pump casing, the drive is often effected via an external motor which is drivingly connected to the pump shaft by a coupling and is received and fastened on a motor stool, which is to say a casing part which is designed for receiving the motor. For this, the one shaft end is sealingly led through the pump casing and out of this, and the other shaft end is mounted within the pump casing. Thereby, it is counted as belonging to the state of the art to accommodate the forces acting upon the pump shaft by way of the motor bearings and to merely provide a radial guiding, for example by way of shaft sleeves which are arranged in the region of the pump stages, within the pump casing. In contrast, the pump-side shaft end is mounted radially and/or axially within the pump casing, in order to relieve the motor bearings, in the case of larger multi-stage pumps. Common to all designs however is an increased loading and thus an increased wear of the motor bearings.
Thereby, it is counted as belonging to the state of the art, to compensate these axial forces upon the shaft which result due to the hydraulic forces, be it by way of subjecting the shaft end mounted in the casing to the pressure of the delivery side or by way of the provision of recesses in the shrouds of the impellers. The latter results in a significant loss in the efficiency, on account of the backflows which are caused by way of this. With hydraulic force compensation, there exists the problem that a highly-loaded seal is to be provided between the rotating shaft end and the stationary casing, which, if it has a good sealing effect, creates a high friction and thus also a high wear and leads to overflow losses given the degradation of the sealing effect.